Theoretical study on the model of metalic melt shearing flow near the surface and its effect on solidification microstructure

Abstract

In this paper, the model of metalic melt shearing flow near the surface is established, and the effect of shearing flow on solidification microstructure of the metal is also analyzed. Calculated results based on A356 alloy melt show that in the laminar flowing melt, the shear stress decreases with increasing length along the vertical direction of the surface of the slope, and the shear stress first decreases rapidly and then stabilizes with increasing length along the flowing direction of the surface of the slope; while in the turbulent flowing melt, the shear stress firstly decreases rapidly and then stabilizes with increasing length along the vertical direction of the surface of the slope, and increases with increasing length along the flowing direction of the surface of the slope. The shear stress at the same position in the melt on the surface of the slope increases with increasing angle of the slope; the shear stress acting on the columnar crystal in the melt on the surface of the slope increases with decreasing length along the vertical direction of the surface of the slope. The shear stress acting on the columnar crystal at the same position in the melt on the surface of the slope increases with increasing angle of the slope; with the increase of the length along the flowing direction, the shear stress acting on the columnar crystal rapidly decreases first and then stabilizes in the laminar flowing melt on the surface of the slope, while the shear stress increases in the turbulently flowing melt on the surface of the slope. Based on the theoretical calculation, the maximum shear stress acting on the columnar crystal in the melt during the shearing flow near the surface of the metalic melt is lower than the yield strength of α-Al grain, so the shear stress induced by shearing flow cannot break the columnar crystal, and only by sweeping the grain into the melt to induce the multiplication of grain, which agrees with the experimental results. So, the proposed model can explain the constitutive relations of the metalic melt shearing flow near the surface and the effect of shear stress on the solidification microstructure.